I couldn't create a user in the Manage Users page.
[stop]Couldn't add user xxx - an unknown error occured.
1. It was because that user was locked, and I didn't see it. The error message
Couldn't add user xxx - User is locked, and you can unlock instead.
2. (Minor) - occured => occurred
3. Noticed that we can still delete users; that should just lock them instead
(and say so).